One suggestion would be preventing collapsing the tree node when AjaxLoadingPanel is displayed. You can declare a global variable and set the value in RequestStart / ResponseEnd accordingly. And in the 'OnClientNodeCollapsing' event check for the variable value to cancel the event. Call the method set_cancel() to specify whether the
event should be cancelled (true) or not (false).

Progress, Telerik, and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries. See Trademarks or appropriate markings.